The present invention relates to a method for processing optical proximity correction, and more particularly, to a method for processing optical proximity correction that uses standardization of an assist pattern which is to be inserted into an outermost pattern for the purpose of enhancing a Depth Of Focus (DOF) margin.
Generally, a semiconductor device is formed on a semiconductor substrate via a photo lithography process. In a conventional photo lithography process, after a photo-resist film is uniformly applied onto a semiconductor substrate. Afterwards the photo-resist film is subjected to an exposure process and subsequently developed to form the photo-resist film pattern which is used as a photo mask to layout the semiconductor device. As an etching object layer below the photo-resist film pattern is etched using the photo-resist film pattern as an etching mask, formation of a specific pattern into the semiconductor substrate is completed.
Such a photo lithography process is becoming increasingly important with an increase in the integration degree of a semiconductor device. This is because the greater the number of cells that should be formed in a limited area, the smaller the critical dimension of a pattern and consequently, the narrower the distance between neighboring patterns, which results in an optical proximity effect by the neighboring patterns. The optical proximity effect may cause distortion of light having passed through a photo mask, making it impossible for a wafer (i.e. the semiconductor substrate) to be exposed according to the layout formed on the photo mask and may result in distorting the desired formed pattern. Therefore, despite the fact that the neighboring patterns should be spaced apart from each other, the completely formed patterns may be connected to each other even though this is unwanted.
Because the optical proximity effect can cause unwanted distortions to the neighboring patterns as described above, then there is a need for technologies related to optical proximity correction. Examples of these technologies include an Optical Proximity Correction (OPC) technology for compensating for diffraction of light using a pattern, and a phase shift mask technology for improving a resolution via an increase in optical contrast. In addition, a chemically amplified resist, which exhibits an excellent photosensitivity with respect to light having a far-ultraviolet wavelength of 248 nm or 194 nm, may be used to achieve an enhanced resolution. There are also various other technologies including, e.g., formation of an assist pattern (as one kind of dummy pattern) that is separated from a main pattern and serves to control an optical proximity effect.
Meanwhile, in development of a semiconductor device, acquiring a sufficient margin when a pattern is formed is very important to substantially prevent a reduction in mass production yield due to defective semiconductor devices brought about by insufficient margins. In particular, as a pattern size is reduced with an increase in the integration degree of a semiconductor device, acquisition of a margin is being emphasized. Here, the term “margin” denotes a process margin with respect to a process for formation of a pattern of a semiconductor device. In more detail, a Depth Of Focus (DOF) margin with respect to an exposure process for formation of a pattern is closely related to a resolution and a critical dimension of a pattern and thus the DOF margin is a very important factor.
To improve a depth of focus, it is generally proposed to insert an assist pattern around an outermost pattern. In this case, rather than inserting the assist pattern around the outermost pattern according to a specific design rule, e.g., a basic shape of the assist pattern is first determined by an experienced engineer and the like and thereafter, assist patterns having superior estimation results are determined via repeated experiments, so as to be inserted into the outermost pattern.
As described above, since the process of inserting the assist pattern for the purpose of improving a depth of focus, i.e. for the purpose of processing optical proximity correction is accomplished via repeated experiments based on engineering know-how, there is a limit with relation to an increase in mask fabrication (S170) time and costs.